Project Summary. Preliminary Data in young, non-obese, human subjects suggest that increasing dietary palmitic acid (PA) lowers daily non-resting energy expenditure, blunts the usual post-exercise rise in energy expenditure, and lowers fatty acid (FA) oxidation, while increasing dietary oleic acid (OA) enhances FA oxidation. However, the differential effects of dietary PA and OA on FA oxidation were greatly exaggerated in females, and the effects of the diets on non-resting energy expenditure were mostly confined to males. Preliminary data from studies in skeletal myocytes indicate that OA preferentially enhances peroxisomal proliferator-activated receptor (PPAR)-mediated induction of p-oxidative genes and that a high PA diet suppresses muscle expression of PPAR X co-activatora (PGC-1a), a transcriptional co-activator of the PPARs that also functions as a master molecular regulator of mitochondrial function. The PPARs are also thought to mediate the repressive effects of unsaturated FA on the expression of stearoyl-CoA desaturase 1 (SCD1), an enzyme that catalyzes endogenous synthesis of OA. SCD1 knockout mice display increased whole-body and muscle fatty acid oxidation and are protected against obesity. Preliminary data show that OA down-regulates mRNA expression of SCD1. Less efficient mitochondrial FA oxidation may cause accumulation of intramyocellular lipids (e.g. diacylglycerol), which inhibits insulin signaling. The following Aims will be assessed in a double-masked, cross-over, feeding trial in 28 healthy, non-obese, adults, 18-40 yr of age, who will be fed in random order both a high PA diet and a high OA diet (each for 3 wk): 1. To investigate transcriptional reprogramming of skeletal muscle in response to a high oleic acid diet (HIOA)compared to a high palmitic acid diet (HI PA), with a focus on gene targets of the PPAR nuclear hormone receptors and the transcriptional co-activator, PGC-1a 2. To correlate diet-induced changes in whole-body fat oxidation and transcriptional reprogramming with systemic and intramuscular levels of various lipid- and mitochondrial-derived metabolites. 3. To measure diet-induced changes in muscle mRNA and protein expression of SCD1, as well as corresponding changes in the desaturation index of muscle lipids. 4. To evaluate the role of gender in modulating transcriptional and metabolic responses to specific dietary FA. Relevance. This project will provide important new information regarding how mitochondrial malfunction, modified by dietary FA, plays a central role in the development of obesity, the metabolic syndrome, type 2 diabetes, and both heritable and age-related metabolic diseases